1. Field of the Invention
The present invention relates to an improvement regarding a steering device in which left and right front wheels and left and right rear wheels are steered by rotation, about the longitudinal axis, of a steering shaft provided to each of the wheels so as to extend inwards along the vehicle width direction.
2. Background Information
Steering devices of such type are able to select, other than the common two-wheel maneuver mode through steering of left and right front wheels only, a variety of maneuver modes such as a sharp-turn mode in which the vehicle performs a sharp turn by reverse-phase-steering the left and right front wheels and the left and right rear wheels, a pivot-turn (on-the-spot-turn) mode in which the vehicle is turned at the present position, or a parallel movement maneuver mode in which all of the left and right front wheels and the left and right rear wheels are similarly steered, and are useful for electric vehicles for which large steering actions are a strong-point.
Steering devices of such description proposed in the past include, e.g., the device disclosed in Japanese Laid-Open Patent Application No. 2007-022159.
In this proposed technique, there are provided a forward/reverse switching mechanism for switching the rotation direction between the left- and right-wheel steering shafts, and a steering gear set for converting the rotation of the left- and right-wheel steering shafts into a rotation about left- and right-wheel kingpin axes in assisting with steering of the left and right wheels, the steering gear set comprising variable speed ratio gears, and non-circular gears in which the pitch curve is changed in two stages are used as the variable speed ratio gears.
According to this steering device, it is possible to operate the forward/reverse switching mechanism to select the required vehicle maneuver mode, i.e., one of the above-mentioned two-wheel maneuver mode, sharp-turn mode, pivot-turn mode, and parallel movement maneuver mode.